The invention relates to a contact detection device comprising:
a first insulating film constituting at least a dome having an internal surface, on which a contact electrode layer is deposited, and an external surface, and
a second insulating film supporting a detection circuit for detecting an electric contact between the contact electrode layer and the detection circuit.
The invention also relates to a data communication apparatus comprising a keyboard and a detection device as mentioned above, as well as to an apparatus comprising a liquid crystal display screen.
The invention further relates to a radiotelephone comprising an apparatus of the above-mentioned type.
The invention is particularly applicable to radiotelephones and portable apparatuses provided with keyboards which can be used in low-luminosity conditions.
European patent application EP 818 793 A1 describes a contact detection device which is uniformly illuminated and is constituted by an upper membrane and a lower membrane. The upper membrane is composed of a synthetic material foil constituted by a plurality of layers, of which one layer of electroluminescent material is sandwiched between a transparent film and an insulating layer. The membrane is molded so as to form domes on its surface. A contact electrode layer is subsequently formed on the insulating layer, on the internal surface of the dome. The lower membrane comprises a foil of insulating material on which an opposite contact electrode layer is formed which is intended to realize an electric contact with the first contact electrode layer.
It is an object of the invention to provide means for realizing a contact detection device comprising an integrated illumination system having a smaller thickness and weight, and a lower manufacturing cost than the known device.
To this end, a device as described in the opening paragraph is characterized in that a layer of electroluminescent material is directly applied on the first film, on a plane surface surrounding said external surface.
In contrast to the known device, the layer of electroluminescent material is not sandwiched in a membrane (the first membrane) and subsequently molded in the mass so as to form a dome. In the device according to the invention, the layer of electroluminescent material is deposited on the first insulating film around or between the external parts which have already been molded. The major drawback of the known device is indeed the difficulty of obtaining a dome by way of molding the membrane without destroying the fragile electroluminescent material. There is a risk that the electroluminescent inks, which are sensitive to heat and the exertion of pressure, are damaged in such a treatment. For this reason, the invention recommends deposition of the electroluminescent ink on a plane surface after formation of the domes.
According to a characteristic feature of the invention, said first and second insulating films are constituted by a folded foil of synthetic material, with said contact electrode layer facing said detection circuit. The functions of detection and illumination of the keyboard are thus completely integrated in a single component of small thickness and weight. An advantage of the invention is that the manufacture of the detection device for the keyboard can thus be entirely subcontracted.
It is another object of the invention to provide a data communication apparatus comprising a keyboard and a detection device as mentioned above, characterized in that each key is associated with a dome for exerting a pressure force on said external surface.
A further object of the invention is to provide a radiotelephone comprising such an apparatus, characterized in that said keyboard comprises parts of a translucent material proximate to the keys so as to be illuminated by said layer of electroluminescent material.
These and other aspects of the invention are apparent from and will be elucidated, by way of non-limitative example, with reference to the embodiments described hereinafter.